Improvement in screw-bolts and nuts



UNITED STATES vPATENT OFFICEo THOMAS EGLISH, OF DULVICH, ENGLAND.

IMPROVEMENT IN SCREW-BOLTS AND NUTS.

Specification forming part of Letters Patent No. 135,898, dated February 18, 1873.

- guished from others of a similar class, together with such parts as I claim and desire to secure by Letters Patentthat is to say:

The object ot' this invention is to diminish the liability of screw-bolts having cylindrical shanks and sunk threads to break in the screwthreads when subjected to a tensile strain. This is effected in either of two ways.

The first method is shown in Figure 1 of the accompanying drawing, which represent-s a seetion ofthe end of a bolt, A, and a nut, B, constructed for this purpose. The screw-thread of the bolt is made ot uniform depth fora certainV distance, from c to a, the rest of the thread, from a to b, is Ina-de of gradually-decreasing depth till it dies out at b. 'lhenut is made with a thread of uniform diameter from c to a, so as to it that portion of the thread ot the bolt. The rest ofthe nut, from u to b, is made with a gradually-increasin g internal diameter, so that the inner edges of its threads tit the bottoms of the threads ot' the bolt. The distance from c to a., throughout which the thread is of uniform depth, is made such thatthe holdingfpower of the screw-thread throughout that distance is equivalent to the tensile strength of the bolt at thebottom of its thread; and the distance from a to c is made such that the holdin g-power oi' the screw-thread throughout that distance is equivalent to the tensile strength of the annular area of the thread of the bolt. Thus the total holding-power of the nut on the bolt being made up of the holdingpower from e to a and of that from a to b is equivalent to the total tensile strength ofthe shank ofthe bolt where it is not weakened by the screwthread. The tapered portions of the threads both of the bolt a-nd of the nut are by preferenceformed by heilig chased in a lathe, the chasing-tool being gradually withform depth from c to a, but the hollow of its thread is lled up gradually more and more from a till it is quite filled up at b. lin this case also the holding-power of the thread from c to a is made equivalent to thetoensile strength of the bolt at the bottom of its thread, while the holding-power of the thread from a to bis made equivalent to the tensile strength of the annular area of the thread of the bolt, the whole holding-power of the -thread being thus equivalent to the tensile strength of the shank or unweakened area of the bolt. The screwthread ot' the bolt is, in this case, by preference formed by a die or dies, and that of the nut is made of uniform diameter either by a tap or by a chasngtool in the lathe, the tops of its threads from (t to b being removed either before or after forming the screw-thread.

The constructions above described are applicable to screw-threads of any pitch or section; but are of greatest advantage when applied to deep threads. The proportions which the uniform parts from c to u bear to the t tpering parts from a to b maybe varied, but the best results are attained when they are proportioned as above described when the nutis screwed onto the bolt as far as it will go. When the nut is not screwed ou so far as to en gage the taper threads the bolt and nut are equivalent to an ordinary bolt and nut, and may be used for all purposes to which ordina-ry bolts and nuts are applied.

It may be readily understood that the nut instead of being made in one piece might he made in two Vparts like a vnut and a lock-nut, the oue part being suited to the tapered thread of the bolt from b to c and the other being uniform to fit the part from a to c.

It may be also understood that the tapering of the thread of the bolt may be effected by a combination of the two methods shown in Figs. l and 2--that is to say, partly by thed ying out of the bQ1t-thread,as` shown in Fig. 1, and part- 1y by filling up the hollow of the bolt-thread, as shown in Fig. 2.

It will be seen that in neither case according to my construction does the diameter of the bolt measured over the tops of its threads vary, while the depth of the thread remains uniform, as in the case of an ordinary tapered bolt. which I do not desire to claim.

The use of bolts and nuts wherein the diameter of the bolt measured at the bottom of its thread increases toward the shank, substantially for the purpose, and in the manner above described.

In testimony whereof I have signed myl Witnesses:

UHAs. D. ABEL, JNO. P. M. MILLARD. 

